From: Mike Meng <meng.yan@...>
Date: 2006-09-17T12:31:05+09:00
Subject: Re: RMagick problem

Thanks to Paul and Timothy.

I've found the problem. I made a stupid mistake when open the URI of an
image file without "b" flag. With "b" flag, everything is ok.

Thanks again.

Mike

Timothy Hunter 写道：

> Mike Meng wrote:
> > Hi all,
> >     I want to determine the geometry of an image. The image file may be
> > in local harddisk or on web. So I use open-uri and
> > Magick::Image::from_blob to do that work, here is the code:
> >
> > open('<path or URI of image file>') { |f|
> >     image = Magick::Image::from_blob(f.read).first
> >     puts "Width: #{image.columns}; Height: #{image.rows}"
> > }
> >
> > For most of the cases, this works well. However, we I tried to read an
> > JPEG generated by my Ricoh Caplio digital camera, it failed and emitted
> > these message:
> >
> > ---------- code ----------
> > E:/workspace/ruby/idapted/testrmg.rb:6:in `from_blob': JPEG datastream
> > contains
> > no image `' (Magick::ImageMagickError)
> >   ....
> > -----------------------------
> >
> >   Surprisingly enough, if I use Magick::Image::read method to read the
> > same image file directly from harddisk, everything is fine, here is the
> > code:
> > ---------- code ----------
> > g = Magick::Image::read('<local file only>').first
> > puts "Width: #{g.columns}; Height: #{g.rows}"
> > -----------------------------
> >
> >   Why do Image::read and Image::from_blob make differeces? How to
> > determine the geometry of  a remote image?
> >
> >   Any comment is appreciated. Thanks!
> >
> >
> >
> Under the covers, #read and #from_blob share most of their code. If
> Image.read can read the file then Image.from_blob can handle it, too.
> The argument to Image.from_blob must be a string containing the entire
> image. I'm guessing that the argument you're giving it is only part of
> the image. Assign f.read to a variable and display its length. Is it the
> same as the size of the image file on disk?